The invention relates to a toothed power transmission belt, but more particularly, the invention relates to a belt with a fabric material as a reinforcement for teeth associated with the belt.
Many power transmission belts have a body of belt material with a plurality of teeth formed of the body along at least one surface of the belt. Such belts may have a tensile member embedded in the body as a load carrying member, and a wear resistant fabric material as a reinforcement at the periphery of the belt surface that includes the belt teeth. The power transmission belt may be in the form of a V-belt such as a variable speed belt where the teeth are in the form of cogs that define belt grooves for enhancing belt flexibility. Another type of toothed belt is a synchronous or timing belt where the belt teeth are designed to engage a toothed pulley to effect power transmission. The fabric material reinforces the teeth for each of these types of belt and provides a wear resistant surface.
A known power transmission belt uses belt teeth in a dual capacity which is to transmit power with a toothed pulley, and to provide belt grooves for enhanced belt flexibility for bending around a small diameter V-pulley. U.S. Pat. No. 1,828,136 discloses a toothed power transmission belt having a V-cross section where the V-sides of the belt engage a small diameter V-pulley and the teeth of the belt engage a large diameter toothed pulley. The belt teeth are covered with a layer of fabric material.
U.S. Pat. No. 4,305,714 discloses a cut-edge, variable speed belt with a plurality of teeth formed along its inside surface which are covered with a fabric material. The teeth define a plurality of grooves which enhance flexibility.
It is known to use a stretchable fabric material when forming teeth in a belt. U.S. Pat. No. 3,078,206 discloses the use of stretchable fabric material in the manufacture of a toothed power transmission belt. A belt sleeve with the stretchable fabric is placed over a toothed mold member and the outside surface of the belt sleeve is pressed with a mold member which displaces belt material and stretches the fabric forcing it into the mold while forming belt teeth. The belt teeth are left with a covering of fabric material.
Early fabrics used for reinforcing belt teeth were in the form of a square woven cotton material. In some cases the cotton was cut on the bias to provide some degree of extensibility. Special fabric materials with a high degree of longitudinal flexibility were developed for toothed belts to enable the belt tooth to be easily formed in the molding process in a manner such as that for U.S. Pat. No. 3,078,206. One form of such fabric is a square woven crimped nylon fabric which has a high degree of stretch. Another example of a specially developed fabric is disclosed in U.S. Pat. No. 4,518,375.
Warp knit fabrics have been used in the manufacture of V-belts to cover teeth. The fabrics while providing some support, have low adherence with belt teeth. An example of a knitted nylon fabric that is used to cover teeth of small size synchronous power transmission belts is disclosed in U.S. Pat. No. 5,427,728.
There is a trend to use square woven, crimped nylon fabric material that was developed for synchronous belts in heavy duty variable speed belts. Such stretchable nylon fabrics reinforce the belt teeth and provide requisite transverse rigidity to inhibit the variable speed belt from turning over when subjected to the transients of a pulley shifting between high and low speeds. The advantage of the stretchable nylon fabric is that it need not be preformed in the belt manufacturing process to form belt teeth. A problem with such nylon fabrics is its inherent instability at temperatures above 340.degree. F. or less if water is present. The nylon fabric melts at approximately 489.degree. F. which may leave residue on the variable speed pulley components when the melted nylon refreezes. Nylon will decompose if water is present. Such high temperatures may be reached when the bottom surface of a variable speed belt slips against a shaft of a variable speed pulley that doubles as a clutch. While square woven fabrics of higher temperature resistant materials could be used in variable speed belts, they typically require the extra processing steps preforming the fabric as part of the belt manufacturing process.
While warp knit nylon fabric is used in V-belts and light duty synchronous belts, it has not found widespread use in V-belts because the warp knit fabric does not have a high adherence to the surfaces of molded belt teeth and the fabric does not have a structure which contributes to transverse reinforcement of a power transmission belt.